17.4% of women with repeat miscarriage have low progesterone

In the mid-luteal
phase, low progesterone level was found in 17.4% and delayed endometrial
development was noted in 27.1% of women. Although women with recurrent
miscarriage women and delayed endometrium had significantly lower
progesterone levels than those with normal endometrial development, only
8/24 had mid-luteal progesterone levels below 30 nmol/L (9.43 ng/ml). http://www.ncbi.nlm.nih.gov/pubmed/11192102

91% of pregnancies with progesterone lower than 15 ng/ml will end in miscarriage

Pregnant women between 5 and 13 weeks'
gestational age were included as Group I who resulted in miscarriage including missed miscarriage, incomplete miscarriage, complete miscarriage and inevitable miscarriage; Group II included normal
pregnancies. When using the free beta-hCG level of <20 ng/ml as a cut
off point, the sensitivity, specificity, positive predictive value and negative predictive value were 91%, 82%, 46%
and 98%, when using a progesterone of <15 ng/ml as a cut off point,
they were 91%, 89%, 59%, 98%. The single measurement of free beta-hCG or
progesterone levels can be useful in the prediction of first trimester miscarriage, but using progesterone may be recommended since
it has high availability and low cost.http://www.ncbi.nlm.nih.gov/pubmed/20373934

Average progesterone in pregnancies that miscarry is 14 ng/ml; in healthy pregnancy: 32ng/ml

In
women between gestation weeks 4 and 12 in whom no apparent signs of a
threatened miscarriage could be diagnosed, risk of miscarriage was
significantly increased in women
at higher age (>33 years), lower body mass index (< or =20 kg/
m(2)) and lower serum progesterone concentrations (< or =12 ng/ml)
prior to the onset of the miscarriage. Women with subsequent miscarriage
also perceived higher levels of stress/demands (supported by higher
concentrations of corticotrophin-releasing hormone) and revealed reduced
concentrations of progesterone-induced blocking factor. These risk
factors were even more pronounced in the subcohort of women recruited
between gestation weeks 4 and 7.http://www.ncbi.nlm.nih.gov/pubmed/18616898

Progesterone over 25 ng/mL at 10 weeks associated with just a 2.15% risk of miscarriage

We determined threshold values for mean gestational sac diameters - crown-rump lengths (> or =10 mm) and progesterone
(> or =25 ng/mL) to predict miscarriage at 10 weeks. For the MGSD-CRL threshold, we can predict that the pregnancy
will continue with 95.78% probability, with 67% sensitivity and 89%
specificity. For the progesterone threshold, the pregnancy will continue with
97.85% probability, with 80% sensitivity and 80% specificity.http://www.ncbi.nlm.nih.gov/pubmed/19708175

Endometrial progesterone levels are 200 times higher in fertile women vs. those who habitually miscarry

Plasma progesterone was two times higher in fertile women than in
habitual miscarriage. In endometrial tissue, progesterone content was 200
times higher in fertile women than in women with habitual miscarriage. Estrogen receptors and progesterone receptors were
lower in the cytosol than in the nuclear fraction in fertile and obese
women. Both receptors were at their lowest level in the cytosol and
nuclear compartment of women with recurrent miscarriage. Fluctuations
mainly in the sex hormone progesterone, in plasma and endometrium
tissue, could interfere with estrogen receptor and progesterone receptor levels.http://www.ncbi.nlm.nih.gov/pubmed/17505942

Low progesterone and low progesterone receptor found in recurrent miscarriage

Estrogen and progesterone receptors in the endometrium of eight
patients with habitual miscarriage in proliferative and secretory phases
were measured. The results showed that the level of serum estrogen was normal in the
proliferative and secretory phases. In 5/8 patients, the serum progesterone level
was below 11 ng/ml. The estrogen receptor of patients was not different
from that of normal women in the proliferative and secretory phases,
but the progesterone receptor was significantly lower than that of
normal women in the proliferative and secretory phases. These suggest
that the lower level of progesterone and progesterone receptor in the
endometrium may be one of the causes of habitual miscarriage.http://www.ncbi.nlm.nih.gov/pubmed/9389036

Along with its endocrine effects, progesterone also acts as an "immunosteroid", by
controlling the bias towards a pregnancy protective immune milieu. A
protein called progesterone-induced blocking factor, by inducing a
Th2 dominant cytokine production mediates the immunological effects of
progesterone. Progesterone plays a role in uterine homing of NK cells
and up-regulates HLA-G gene expression, the ligand for various NK
inhibitory receptors. At high concentrations, progesterone is a potent
inducer of Th2-type cytokines as well as of LIF and M-CSF production by T
cells. http://www.ncbi.nlm.nih.gov/pubmed/17981685

Women who miscarry may have an inappropriate immune response to progesterone

In a longitudinal
prospective study, the wheal and flare reaction (allergic reaction) after intradermal
injection of estrogen and progesterone was compared in 29 women with
recurrent miscarriage to the response in 10 healthy women. Estrogen
hypersensitivity was found in 23 patients, and progesterone
hypersensitivity in 20 patients. No patient in the control group
demonstrated sex hormone hypersensitivity. CONCLUSION: Recurrent miscarriage may be associated with inappropriate local immune
responses to sex hormones. Further research is necessary into the
mechanisms of hypersensitivity to estrogen and progesterone and their
interactions with other systems.http://www.ncbi.nlm.nih.gov/pubmed/17217371

In the repeat miscarriage group, the uterine blood flow resistance in the uterine artery of women with antinuclear antibodies (high in autoimmune disease)
was
significantly higher than that of women without antinuclear antibodies.
Among women without antinuclear antibodies, the mean uterine blood flow
resistance in the repeat miscarriage group (2.44) was also
significantly higher than in the control group (2.19). The uterine blood
flow resistance was inversely correlated with serum progesterone
levels. CONCLUSIONS: Elevated
uterine arterial impedance is associated with repeat miscarriage. http://www.ncbi.nlm.nih.gov/pubmed/11756386

Progesterone reduces the effect of coagulation factors and is primary marker for miscarriage risk